The present invention generally relates to pressure regulating devices, and more particularly to pilots for controlling such devices.
The use of pilots to control pressure regulating valves is well known in the art. A pressure regulating valve typically includes a valve body having an upstream inlet and a downstream outlet. A throttling member such as a plug is disposed between the inlet and the outlet and engages a seat formed in the valve body. A stem attached to the plug engages an actuator, which moves the stem and attached plug between open and closed positions.
The pilot is used to control the actuator according to a control parameter, such as downstream fluid pressure. The pilot typically includes a pilot valve body having an inlet, an outlet, and a valve seat disposed between the inlet and outlet. A pilot throttling member is positioned to engage the pilot seat, and a pilot stem is attached to the pilot throttling member. The pilot stem typically engages a flexible diaphragm which is biased towards an open position in which fluid flow is allowed through the pilot. The outlet of the pilot is connected to the downstream fluid piping so that the downstream pressure registers at the pilot. The inlet of the pilot is attached to upstream fluid piping through a restricter. Between the pilot inlet and the restricter, a control pressure branch extends to the pressure control valve to provide a control pressure for the actuator.
In operation, when the downstream fluid pressure exceeds a desired set point, the pilot throttling member moves toward a closed position, thereby directing inlet pressure toward the control valve actuator. In response, the actuator pushes the plug toward the closed position to reduce fluid flow through the valve, thereby reducing downstream pressure. When downstream pressure drops below the desired set point, the pilot throttling member moves toward the open position to reduce the inlet pressure directed toward the actuator. In response, the actuator moves the plug to an open position to increase flow through the valve, thereby increasing downstream pressure. The pilot throttling member is at least partially open most of the time. As a result, process fluid bleeds through the pilot and is discharged either to atmosphere or to the downstream fluid piping. Bleeding to atmosphere results in lost product, while bleeding to the downstream fluid piping introduces an uncontrolled volume of fluid downstream of the valve.
Certain devices have been proposed which reduce the bleeding through the pilot. Becker Precision Equipment, Inc., for example, has proposed a valve regulator pilot for use with a double-acting cylinder actuator for use in pressure control applications. The actuator includes a chamber having a piston which is mechanically linked to a valve actuating arm. The piston divides the chamber into upper and lower chamber sections, each section having a pressure port. The pilot includes a pair of pistons, each piston controlling pressure flow into an associated one of the upper and lower chamber sections. The pilot pistons move according to the differential between pilot supply pressure and discharge pressure and, accordingly, vary the pressures supplied to the upper and lower chambers sections. The relative pressures in the upper and lower chamber sections drive the piston to adjust the valve. The use of two pilot pistons, as well as separate restricters located upstream of the pilot, however, significantly increases the response time of the pilot.
In view of the foregoing, a pilot for use with a pressure regulating device is desired which minimizes bleeding and reduces response time.
In accordance with certain aspects of the present invention, a control valve assembly is provided for a main line transporting a fluid. The control valve assembly comprises a control valve and an actuator adapted to actuate the control valve. The actuator includes a dome and a pressure surface disposed inside the dome to define first and second chambers of the dome, the pressure surface moving in response to a pressure differential between the first and second chambers. A pilot valve is provided having a first connection port, a second connection port, a first control port, a second control port, and a pressure responsive valve member. A first passageway communicates the fluid at a first pressure from the main flow line to the first connection port. A second passageway communicates the fluid at a second pressure from the main flow line to the second connection port, the second pressure being different than the first pressure. A third passageway extends between the first control port and the first chamber of the actuator. A fourth passageway extends between the second control port and the second chamber of the actuator. The pressure responsive valve is adapted to move in response to the second pressure between a first position, in which the first passageway fluidly communicates with the third passageway and the second passageway fluidly communicates with the fourth passageway, and a second position, in which the first passageway fluidly communicates with the fourth passageway, and the second passageway fluidly communicates with the third passageway.
In accordance with additional aspects of the present invention, a control valve assembly is provided for use in a main flow line transporting fluid. The control valve assembly comprises a control valve adapted to be disposed in the main flow line and an actuator having a dome. A pressure surface is disposed inside the dome for actuating the control valve between open and closed positions, the pressure surface dividing the dome into first and second chambers. A pilot valve is provided having an inlet in fluid communication with an upstream portion of the main flow line, an outlet in fluid communication with a downstream portion of the main flow line, a first control pressure port in fluid communication with the actuator first chamber, a second control pressure port in fluid communication with the actuator second chamber, and a pressure responsive valve in fluid communication with the pilot valve outlet. The pressure responsive valve is movable between a first position, in which the inlet fluidly communicates with the first control pressure port and the outlet fluidly communicates with the second pressure control port, and a second position, in which the inlet fluidly communicates with the second pressure control port, and the outlet fluidly communicates with the first pressure control port.
In accordance with further aspects of the present invention, a pilot valve is provided for a control valve disposed in a main flow line. The pilot valve comprises an inlet fluid chamber in fluid communication with fluid to be controlled in the main flow line on one side of the control valve, and an outlet fluid chamber in fluid communication with the main flow line on an opposite side of the control valve. A first control fluid chamber is in fluid communication with one side of a pressure surface in the control valve, and a second control fluid chamber fluidly communicates with an opposite side of a pressure surface in the control valve. A diaphragm is disposed inside the outlet fluid chamber and movable in response to an outlet fluid pressure between a lockup position and a flow position. A passage is formed in the pilot valve to establish fluid communication between the inlet fluid chamber and the first control fluid chamber. An insert defining a valve seat is positioned between the inlet fluid chamber and the second control fluid chamber, while a slidable valve body is supported for movement with the diaphragm. The valve body has a central passage with a lower end in fluid communication with the first control fluid chamber and an enlarged valve portion. The passage is unobstructed and the enlarged valve portion engages the insert valve seat when the diaphragm is in the lockup position, and the enlarged valve portion is spaced from the insert valve seat and the passage is blocked when the diaphragm is in the flow position. A stationary collar defines an orifice establishing fluid communication between the outlet fluid chamber and the second control fluid chamber. A stationary stop member defines a valve seat positioned between the outlet fluid chamber and an upper end of the central passage. A movable collar is supported for movement with the diaphragm and defines an orifice. The movable collar engages the stationary stop member valve seat to cut off flow through the movable collar orifice when the diaphragm is in the lockup position, and the movable collar engages the stationary collar to cut off flow through the stationary collar orifice when the diaphragm is in the flow position.